In extracorporeal blood processing, blood is taken out of a human subject, processed (e.g. treated) and then reintroduced into the subject by means of an extracorporeal blood flow circuit (“EC circuit”) which is part of a machine for blood processing. Generally, the blood is circulated through the EC circuit by a blood pump. In certain types of extracorporeal blood processing, the EC circuit includes an access device for blood withdrawal (e.g. an arterial needle or catheter) and an access device for blood reintroduction (e.g. a venous needle or catheter), which are inserted into a dedicated blood vessel access (e.g. fistula or graft) on the subject. The access devices form a fluid connection between the EC circuit and the cardiovascular system of the subject. This type of EC circuit is, e.g., used in extracorporeal blood treatments such as hemodialysis, hemodiafiltration, hemofiltration, plasmapheresis, bloodbanking, blood fraction separation (e.g. cells) of donor blood, apheresis, extracorporeal blood oxygenation, assisted blood circulation, extracorporeal liver support/dialysis, ultrafiltration, etc.
It is vital to minimize the risk for malfunctions in the fluid connection that may lead to a potentially life-threatening condition of the subject. A particularly serious condition may arise if the EC circuit is disrupted downstream of the blood pump while the blood pump is running, e.g. by the access device for blood reintroduction coming loose from the blood vessel access. Such a venous-side disruption, which is commonly referred to as a Venous Needle Dislodgement (VND), may cause the subject to be drained of blood within minutes. A disruption on the arterial side, e.g. by the access device for blood withdrawal coming loose from the blood vessel access, may also present a patient risk, by air being sucked into the EC circuit and transported into the cardiovascular system.
Machines for extracorporeal blood treatment typically include a safety system that monitors the status of the fluid connection between the EC circuit and the subject and triggers an alarm and/or an appropriate safety action whenever a potentially dangerous situation is detected. Such safety systems may operate on pressure signals from pressure sensors in the EC circuit. Conventionally, VND detection is carried out by comparing one or more measured average pressure levels with one or more threshold values. However, it may be difficult to set appropriate threshold values, since the average pressure in the EC circuit may vary between treatments and between subjects, and also during a treatment, e.g. as a result of the patient moving. Further, if an access device comes loose and gets stuck in bed sheets or the patient's clothes, the measured average pressure might not change enough to indicate the potentially dangerous situation.
To overcome these drawbacks, various techniques have been proposed for detecting VND by identifying absence of dedicated pulsations, which originate from the subject, in a pressure signal from a pressure sensor (“venous pressure sensor”) on the downstream side of the blood pump in the EC circuit, e.g. in WO97/10013, US2005/0010118, WO2009/156174, WO2010/149726 and US2010/0234786. The dedicated pulsations may e.g. originate from the heart or the breathing system. These known VND detection techniques presume that the heart or breathing pulses can be reliably detected in the pressure signal. To enable reliable detection, it may be necessary to filter the pressure signal to essentially remove all signal interferences. In practice, the accuracy and robustness of the VND detection relies on the efficiency and stability of the filtering technique used for cleaning the pressure signal from signal interferences. The signal interferences typically comprise strong pressure pulsations (“pump pulses”) originating from the blood pump, and may also comprise further interfering pressure pulsations, e.g. caused by further pumps, valves, balancing chambers, etc in the EC circuit. It may be a challenging task to remove e.g. the pump pulses, since the rate of the heart pulses and the rate of the blood pump, i.e. the blood flow through the EC circuit, may change over time. If the rate of heart pulses matches the rate of pump pulses, it is not unlikely that the filtering will fail. Complete removal of the pump pulses is also rendered difficult by the fact that the pump pulses generally are much stronger than the heart and breathing pulses in the pressure signal. An advanced filtering technique may thus be required, increasing complexity and potentially introducing stability and convergence issues.
There is a continued need to achieve an improved technique for detecting a disruption of the fluid connection on the arterial side and/or the venous side of the EC circuit, in terms of one or more of the following: ability to handle overlap in frequency and/or time between pump pulses and heart pulses, complexity of the detection technique, response time, processing efficiency and memory usage of the detection technique, accuracy of detection, and robustness of detection.
Corresponding needs may arise in other fields of technology. Thus, generally speaking, there is a need for an improved or alternative technique for detecting a disruption of a fluid connection between a first fluid containing system and a second fluid containing system, based on at least one pressure signal acquired from a set of pressure sensors in the first fluid containing system.